Cloning and characterization of α1H from human heart, a member of the T-type Ca2+ channel gene family

Voltage-activated Ca(2+) channels exist as multigene families that share common structural features. Different Ca(2+) channels are distinguished by their electrophysiology and pharmacology and can be classified as either low or high voltage-activated channels. Six alpha 1 subunit genes cloned previously code for high voltage-activated Ca(2+) channels; therefore, we have used a database search strategy to identify new Ca(2+) channel genes, possibly including low voltage-activated (T-type) channels. A novel expressed sequence-tagged cDNA clone of alpha 1G was used to screen a cDNA library, and in the present study, we report the cloning of alpha 1H (or Ca(v)T.2), a low voltage-activated Ca(2+) channel from human heart. Northern blots of human mRNA detected more alpha 1H expression in peripheral tissues, such as kidney and heart, than in brain. We mapped the gene, CACNA1H, to human chromosome 16p13.3 and mouse chromosome 17. Expression of alpha 1H in HEK-293 cells resulted in Ca(2+) channel currents displaying voltage dependence, kinetics, and unitary conductance characteristic of native T-type Ca(2+) channels. The alpha 1H channel is sensitive to mibefradil, a nondihydropyridine Ca(2+) channel blocker, with an IC(50) of 1.4 mu mol/L, consistent with the reported potency of mibefradil for T-type Ca(2+) channels. Together with alpha 1G, a rat brain T-type Ca(2+) channel also cloned in our laboratory, these genes define a unique family of Ca(2+) channels.